Defense Secretary Donald Rumsfeld has criticized the Iranian government, saying it is not stopping the flow of weapons across its border into Iraq.  The criticism follows recent reports that Iraqi border guards intercepted shipments of highly sophisticated bombs from Iran.

At a Pentagon news conference Tuesday, Secretary Rumsfeld said the evidence is conclusive that weapons from Iran are entering Iraq. 

"It is true that weapons - clearly, unambiguously from Iran have been found in Iraq," he said.

Mr. Rumsfeld said U.S. officials do not know if the Iranian government is linked to the weapons shipments, or if it is the work of independent militant groups. But he said the government in Tehran should do more to stop weapons from crossing the nearly 1,500 kilometer long border with Iraq.

"It's a big border and it's notably unhelpful for the Iranians to be allowing weapons of those types to cross the border," Mr. Rumsfeld added.

Military officials have voiced concern over the discovery of increasingly sophisticated explosive devices including so-called shape charges that can penetrate armored vehicles. In recent days U.S. officials said Iraqi border guards have intercepted several shipments of such devices from Iran.

Mr. Rumsfeld also warned insurgents may step-up attacks during the next several months with the approach of several political milestones for Iraq.

"I think it's reasonable to expect that violence could indeed increase for a time as it did during the last elections. But given the political progress that should not necessarily be an accurate gauge of the enemy's future," he explained.

Iraqi officials are expected to submit a draft constitution on Monday. A referendum on the document is scheduled for October 15. Then, on December 15, Iraqi officials plan to hold national elections for the government outlined in the constitution.

Mr. Rumsfeld urged Iraqi officials to stick to the planned timetable for drafting the constitution. He said the document is a critical step in persuading Iraqis their country is worth fighting for and they have a stake in its future.